Chris, Without going in to deeper details, the fix is to enable event 10170 to enable the old costing algorithms. Set the event 10170 (for session level), this is a change behavior event, quite safe. -Gopal On Sat, May 31, 2014 at 10:21 AM, Chris Saxon <chris.saxon@xxxxxxxxx> wrote: > Hi, > > I've been testing using bitmap indexes on 11.2.0.2 EE. When joining two > tables on a column with a BTree index, the index is used in the execution > plan. If this index is changed to a bitmap index, Oracle no longer uses the > index when executing the query! It assigns a higher cost to using the > bitmap index when joining, despite this being a cheaper approach (in terms > of consistent gets). > > To see this, I created a date dimension table with 515 days (rows) and a > sales fact table with 1,000 rows for each day: > > create table date_d ( > date_id integer not null primary key, > calendar_date date not null unique > ); > > create table sales_fact ( > date_id integer not null > references date_d (date_id), > quantity number not null, > total_value number not null > ); > > insert into date_d > select rownum, date'2013-01-01'-1+rownum > from dual > connect by level <= sysdate - date'2013-01-01'; > > insert into sales_fact > with rws as (select * from dual connect by level <= 1000) > select d.date_id, round(dbms_random.value(1, 20)), > round(dbms_random.value(10, 100), 2) > from date_d d > cross join rws > order by d.date_id; > > begin > dbms_stats.gather_table_stats(user, 'sales_fact'); > dbms_stats.gather_table_stats(user, 'date_d'); > end; > / > > If I create a BTree index on SALES_FACT.DATE_ID, then join from the date > dim to the fact table, restricting to two days, Oracle uses the index on > the fact table as I would expect (as we're fetching 2,000 of 515,000 rows): > > create index safa_date_id on sales_fact (date_id); > > set autotrace trace > select s.* from sales_fact s join date_d d > on d.date_id = s.date_id > where calendar_date between date'2013-12-31' and date'2014-01-01'; > > set autotrace off > > Execution Plan > ---------------------------------------------------------- > Plan hash value: 2189554905 > > > ---------------------------------------------------------------------------------------------- > | Id | Operation | Name | Rows | Bytes | > Cost (%CPU)| Time | > > ---------------------------------------------------------------------------------------------- > | 0 | SELECT STATEMENT | | 3002 | 69046 | > 21 (0)| 00:00:01 | > | 1 | NESTED LOOPS | | | | > | | > | 2 | NESTED LOOPS | | 3002 | 69046 | > 21 (0)| 00:00:01 | > | 3 | TABLE ACCESS BY INDEX ROWID| DATE_D | 3 | 36 | > 3 (0)| 00:00:01 | > |* 4 | INDEX RANGE SCAN | SYS_C0037151 | 3 | | > 2 (0)| 00:00:01 | > |* 5 | INDEX RANGE SCAN | SAFA_DATE_ID | 1000 | | > 3 (0)| 00:00:01 | > | 6 | TABLE ACCESS BY INDEX ROWID | SALES_FACT | 1000 | 11000 | > 6 (0)| 00:00:01 | > > ---------------------------------------------------------------------------------------------- > > Predicate Information (identified by operation id): > --------------------------------------------------- > > 4 - access("D"."CALENDAR_DATE">=TO_DATE(' 2013-12-31 00:00:00', > 'syyyy-mm-dd > hh24:mi:ss') AND "D"."CALENDAR_DATE"<=TO_DATE(' 2014-01-01 > 00:00:00', 'syyyy-mm-dd > hh24:mi:ss')) > 5 - access("D"."DATE_ID"="S"."DATE_ID") > > > Statistics > ---------------------------------------------------------- > 1 recursive calls > 0 db block gets > 290 consistent gets > 6 physical reads > 0 redo size > 36195 bytes sent via SQL*Net to client > 1839 bytes received via SQL*Net from client > 135 SQL*Net roundtrips to/from client > 0 sorts (memory) > 0 sorts (disk) > 2000 rows processed > > However, if I drop the normal index and re-create it as a bitmap index the > query above changes to a FTS on the SALES_FACT table: > > set autotrace off > drop index safa_date_id; > create bitmap index safa_date_id on sales_fact (date_id); > > set autotrace trace > select s.* from sales_fact s join date_d d > on d.date_id = s.date_id > where calendar_date between date'2013-12-31' and date'2014-01-01'; > > Execution Plan > ---------------------------------------------------------- > Plan hash value: 525754326 > > > --------------------------------------------------------------------------------------------- > | Id | Operation | Name | Rows | Bytes | Cost > (%CPU)| Time | > > --------------------------------------------------------------------------------------------- > | 0 | SELECT STATEMENT | | 3002 | 69046 | > 315 (2)| 00:00:04 | > |* 1 | HASH JOIN | | 3002 | 69046 | > 315 (2)| 00:00:04 | > | 2 | TABLE ACCESS BY INDEX ROWID| DATE_D | 3 | 36 | > 3 (0)| 00:00:01 | > |* 3 | INDEX RANGE SCAN | SYS_C0037151 | 3 | | > 2 (0)| 00:00:01 | > | 4 | TABLE ACCESS FULL | SALES_FACT | 515K| 5532K| > 310 (1)| 00:00:04 | > > --------------------------------------------------------------------------------------------- > > Predicate Information (identified by operation id): > --------------------------------------------------- > > 1 - access("D"."DATE_ID"="S"."DATE_ID") > 3 - access("D"."CALENDAR_DATE">=TO_DATE(' 2013-12-31 00:00:00', > 'syyyy-mm-dd > hh24:mi:ss') AND "D"."CALENDAR_DATE"<=TO_DATE(' 2014-01-01 > 00:00:00', 'syyyy-mm-dd > hh24:mi:ss')) > > > Statistics > ---------------------------------------------------------- > 1 recursive calls > 0 db block gets > 1267 consistent gets > 0 physical reads > 0 redo size > 36195 bytes sent via SQL*Net to client > 1839 bytes received via SQL*Net from client > 135 SQL*Net roundtrips to/from client > 0 sorts (memory) > 0 sorts (disk) > 2000 rows processed > > If we hint the query to use the bitmap index, we can see it has a higher > cost. The autotrace stats report significantly fewer consistent gets though: > > Execution Plan > ---------------------------------------------------------- > Plan hash value: 1520624055 > > > ---------------------------------------------------------------------------------------------- > | Id | Operation | Name | Rows | Bytes | > Cost (%CPU)| Time | > > ---------------------------------------------------------------------------------------------- > | 0 | SELECT STATEMENT | | 3002 | 69046 | > 416 (0)| 00:00:05 | > | 1 | NESTED LOOPS | | | | > | | > | 2 | NESTED LOOPS | | 3002 | 69046 | > 416 (0)| 00:00:05 | > | 3 | TABLE ACCESS BY INDEX ROWID| DATE_D | 3 | 36 | > 3 (0)| 00:00:01 | > |* 4 | INDEX RANGE SCAN | SYS_C0037151 | 3 | | > 2 (0)| 00:00:01 | > | 5 | BITMAP CONVERSION TO ROWIDS| | | | > | | > |* 6 | BITMAP INDEX SINGLE VALUE | SAFA_DATE_ID | | | > | | > | 7 | TABLE ACCESS BY INDEX ROWID | SALES_FACT | 1000 | 11000 | > 416 (0)| 00:00:05 | > > ---------------------------------------------------------------------------------------------- > > Predicate Information (identified by operation id): > --------------------------------------------------- > > 4 - access("D"."CALENDAR_DATE">=TO_DATE(' 2013-12-31 00:00:00', > 'syyyy-mm-dd > hh24:mi:ss') AND "D"."CALENDAR_DATE"<=TO_DATE(' 2014-01-01 > 00:00:00', 'syyyy-mm-dd > hh24:mi:ss')) > 6 - access("D"."DATE_ID"="S"."DATE_ID") > > > Statistics > ---------------------------------------------------------- > 1 recursive calls > 0 db block gets > 152 consistent gets > 1 physical reads > 0 redo size > 36195 bytes sent via SQL*Net to client > 1839 bytes received via SQL*Net from client > 135 SQL*Net roundtrips to/from client > 0 sorts (memory) > 0 sorts (disk) > 2000 rows processed > > If you remove the join to the date dim and just use the date ids, Oracle > uses the index as expected: > > select * from sales_fact > where date_id between 365 and 366; > > Execution Plan > ---------------------------------------------------------- > Plan hash value: 2749560877 > > > --------------------------------------------------------------------------------------------- > | Id | Operation | Name | Rows | Bytes | Cost > (%CPU)| Time | > > --------------------------------------------------------------------------------------------- > | 0 | SELECT STATEMENT | | 3002 | 33022 | > 221 (0)| 00:00:03 | > | 1 | TABLE ACCESS BY INDEX ROWID | SALES_FACT | 3002 | 33022 | > 221 (0)| 00:00:03 | > | 2 | BITMAP CONVERSION TO ROWIDS| | | | > | | > |* 3 | BITMAP INDEX RANGE SCAN | SAFA_DATE_ID | | | > | | > > --------------------------------------------------------------------------------------------- > > Predicate Information (identified by operation id): > --------------------------------------------------- > > 3 - access("DATE_ID">=365 AND "DATE_ID"<=366) > > > Statistics > ---------------------------------------------------------- > 1 recursive calls > 0 db block gets > 144 consistent gets > 0 physical reads > 0 redo size > 36195 bytes sent via SQL*Net to client > 1839 bytes received via SQL*Net from client > 135 SQL*Net roundtrips to/from client > 0 sorts (memory) > 0 sorts (disk) > 2000 rows processed > > Looking at the 10053 trace, I can see this is because the bm index join > cost is calculated as higher than the FTS of SALES_FACT: > > NL Join > Outer table: Card: 3.00 Cost: 3.00 Resp: 3.00 Degree: 1 Bytes: 12 > Access path analysis for SALES_FACT > Inner table: SALES_FACT Alias: S > Access Path: TableScan > NL Join: Cost: 929.82 Resp: 929.82 Degree: 1 > Cost_io: 920.00 Cost_cpu: 317629069 > Resp_io: 920.00 Resp_cpu: 317629069 > ****** trying bitmap/domain indexes ****** > Access Path: index (AllEqJoinGuess) > Index: SAFA_DATE_ID > resc_io: 1.00 resc_cpu: 8171 > ix_sel: 0.001942 ix_sel_with_filters: 0.001942 > NL Join : Cost: 6.00 Resp: 6.00 Degree: 1 > Cost_io: 6.00 Cost_cpu: 47359 > Resp_io: 6.00 Resp_cpu: 47359 > Bitmap nodes: > Used SAFA_DATE_ID > Cost = 6.001464, sel = 0.001942 > Access path: Bitmap index - accepted > Cost: 416.121488 Cost_io: 415.999594 Cost_cpu: 3943626.145192 Sel: > 0.001942 > Not Believed to be index-only > ****** finished trying bitmap/domain indexes ****** > > Best NL cost: 416.12 > resc: 416.12 resc_io: 416.00 resc_cpu: 3943626 > resp: 416.12 resp_io: 416.00 resc_cpu: 3943626 > > However, same section of the 10053 trace shows the following when using a > BTree index on the SALES_FACT.DATE_ID column: > > NL Join > Outer table: Card: 3.00 Cost: 3.00 Resp: 3.00 Degree: 1 Bytes: 12 > Access path analysis for SALES_FACT > Inner table: SALES_FACT Alias: S > Access Path: TableScan > NL Join: Cost: 929.82 Resp: 929.82 Degree: 1 > Cost_io: 920.00 Cost_cpu: 317629069 > Resp_io: 920.00 Resp_cpu: 317629069 > Access Path: index (AllEqJoinGuess) > Index: SAFA_DATE_ID > resc_io: 6.00 resc_cpu: 433579 > ix_sel: 0.001942 ix_sel_with_filters: 0.001942 > NL Join : Cost: 21.04 Resp: 21.04 Degree: 1 > Cost_io: 21.00 Cost_cpu: 1323580 > Resp_io: 21.00 Resp_cpu: 1323580 > > Best NL cost: 21.04 > resc: 21.04 resc_io: 21.00 resc_cpu: 1323580 > resp: 21.04 resp_io: 21.00 resc_cpu: 1323580 > > Why does this happen? Is this a bug or expected behaviour? > > Thanks, > Chris > www.sqlfail.com >